利用MC-ICPMS精确测定^(143)Nd/^(144)Nd和Sm/Nd比值  

Precise measurement of ^(143)Nd/^(144)Nd and Sm/Nd ratios using multiple collectors inductively coupled plasma mass spectrometer (MC ICPMS)

作　　者：梁细荣[1] 韦刚健[1] 李献华[1] 刘颖[1] 

机构地区：[1]中国科学院广州地球化学研究所,广东广州510640

出　　处：《地球化学》2003年第1期91-96,共6页Geochimica

基　　金：中国科学院知识创新工程重要方向性项目(KZCX2-102;KZXC2-101)

摘　　要：多收集器等离子体质谱(MC-ICPMS)用于分析Sm-Nd同位素时,质量分馏系数(β)与同位素的质量数呈线性关系。可以采用两种方法进行质量分馏校正:双分馏系数内部校正法(DFIC)和单分馏系数外部校正法(SFEC)。采用DFIC法,对国际标样Shin-EtsuJNdi-1和实验室标样Nd-GIG进行了为期五个月的143Nd/144Nd比值测量统计,结果分别为0.512120±0.000012(2σSD)、0.511532±0.000013(2σSD)。采用SFEC法,对Nd-GIG标样的测量统计结果为0.511525±0.000015(2σSD)。两种方法的测量结果在分析误差范围内与其推荐值或TIMS测量值完全一致。对加Ce和Sm的Nd-GIG混合溶液分别进行了Ce和Sm对143Nd/144Nd比值分析的干扰校正研究和Sm/Nd比值测量,结果显示,143Nd/144Nd比值分别与Ce/Nd、Sm/Nd测量值呈线性关系,Sm/Nd测量值与其质量比值亦呈很好的线性关系。这表明利用MC-ICPMS可以快速精确地测定存在Ce、Sm干扰的样品的143Nd/144Nd比值,同时可获得精确的Sm/Nd比值,而无需加入稀释剂。这就使直接测定地质样品的Sm-Nd等时线年龄成为可能。Mass fractionations in the measurement for 143Nd/144Nd and Sm/Nd isotopic ratios bya multiple collectors inductively coupled plasma mass spectrometer (MC ICPMS) are mass dependent, to which a modified exponential law and external calibration are confirmed for the calibration. Two methods are defined and applied tothe mass fractionation: (1) Double fractionation internal correction (DFIC), and (2) single fractionation external correction (SFEC). The five month measured143Nd/144Nd ratios by DFIC method for the Shin Etsu JNdi 1, and the Nd GIG, an internal laboratory neodymium isotopic reference, are 0.512 120±0.000 012 (2σSD) and ±0.000 013 (2σSD), respectively; while the 143Nd/144Nd ratios by SFEC method for the Nd GIG is ±(2σSD). These results are accordant in range of the analytical error with their recommended or TIMS measured values. Measurements of five Nd GIG solutions added cerium with Ce/Nd mass ratios from 0.05 to 1.50 reveal a negative linear correlation between the measured 140Ce/146Nd and 143Nd/144Nd ratios. While the measurements of six Nd GIG solution added samarium with Sm/Nd ratios from 0.05 to 0.70 display a positive linear correlation between the measured 147Sm/146Nd and 143Nd/144Nd ratios, the measured 147Sm/146Nd ratio also has a closely positive linear correlation with the Sm/Nd mass ratios. Consequently, the true 143Nd/144Nd ratios and Sm/Nd mass ratios can be extrapolated by substituting the variables with the measured 147Sm/146Nd or 140Ce/146Nd ratios. Our results indicate that the analytical methods are efficient to get the precise and accurate 143Nd/144Nd ratio for samples with remains of cerium and or samarium; and that they are effective to get the accurate Sm/Nd ratio for samarium nonseparated samples, without isotopic dilution. This study revealed a possible approach to directly measuring the Sm Nd isochron ages on geological samples.

关 键 词：MC-ICPMS 多收集器等离子体质谱 钐同位素 钕同位素 双分馏系数内部校正法 单分馏系数外部校正法 

分 类 号：P597[天文地球—地球化学]